Crop yield response to water - Cra

Figure 2Reproductive growth of pear trees.220200Stage IStage IIFruit fresh mass (grams)180160140120100806040LSD 0.0520013-Apr.3-May23-May12-June 2-July 22-July11-Aug.31-Aug.DateEarly vegetative and reproductive growth; growth Stage IPear flowers commonly open almost synchronously with leaf appearance. Shoot growthstarts after first leaf appearance and occurs concomitantly with the current seasonreproductive growth. Vigour-conditions will determine the extent and the timing of shootgrowth enlargement. In trees grafted on vigour controlling rootstocks such as quince, shootdevelopment occurs in one-to-two flushes during spring (April and May in the NorthernHemisphere). Under more vigorous conditions shoot growth extends into early summerthroughout all Stage I. At this time, vegetative growth of the scion is a stronger sink than fruit,and fruit growth is quite slow in terms of dry mass accumulation. Root growth in spring is alsorelevant and occurs concomitantly with shoot development and ceases near the end of May.Root growth, however, depends on inter-organ competition and availability of carbohydrates.The end of rapid shoot growth is signalled by the appearance of a terminal bud.Fruit growth starts right after ovary fertilization and this can be measured in the field at aboutone month after full bloom. Physiological fruit drop, however, lasts longer and can extenduntil the end of Stage I or onset of Stage II (in midseason cultivars). Stage I corresponds to thefruit main cell-division period, and takes place during the first 7 to 8 weeks after bloom (Bain,1961). The remainder of fruit development constitutes Stage II when the major increase in cellvolume occurs (Bain, 1961). Cell expansion, however, is also active during Stage I, but its effectis masked by the simultaneous occurrence of cell division.Fruit growth during Stage IIExpansive fruit growth is the main growth event for the tree during Stage II. Stage IIcorresponds to the period of rapid fruit cell enlargement. Nevertheless, bud development alsobecomes relevant after cessation of shoot enlargement. Differentiation of buds into flowerbuds usually occurs at the beginning of Stage II in midseason cultivars (early to mid-June)378crop yield response to water